Method for reducing dust during handling of reactive form coke briquettes

ABSTRACT

BRIQUETTES OF REACTIVE FORM COKE ARE TREATED BY APPLYING AN AQUEOUS AGENT CONTAINING A LIGNOSULFONATE WHILE THE BRIQUETTES ARE AT AN ELEVATED TEMPERATURE IN THE RANGE 100-200*F. AQUEOUS AGENT MAY CONTAIN AN ALKALINE OXIDE (CAO OR MGO). BRIQUETTES DRY WHILE COOLING FROM ELEVATED TEMPERATURE TO FORM AN ADHERENT FILM OF LIGNOSULFONATE ON BRIQUETTES. ALKALINE OXIDE IN FILM IS REACTED WITH CO2 TO FORM A CARBONATE IN FILM. FILM PREVENTS DUSTING DURING HANDLING.

United States Patent ABSTRACT OF THE DISCLOSURE Briquettes of reactive form coke are treated by applylng an aqueous agent containing a lignosulfonate while the briquettes are at an elevated temperature in the range 100-200 F. Aqueous agent may contain an alkaline oxide (CaO or MgO). Briquettes dry while cooling from elevated temperature to form an adherent film of lignosulfonate on briquettes. Alkaline oxide in film is reacted v with CO to form a carbonate in film. Film prevents dusting during handling.

BACKGROUND OF THE INVENTION The present invention relates generally to methods for reducing dust during handling of coke, and more particularly to a method for treating briquettes of reactive form coke to reduce dust therefrom during handling following processing in a coke-making unit.

Coke has substantial usage as a raw material in metallurgical operations, such as blast furance processes. At large integrated steel works the coke is manufactured locally in coke-making units. For smaller plants, the coke is manufactured elsewhere and shipped in, e.g., by rail. Conventional coke is discharged from the coke-makmg unit as a mass of lumps of irregular shape. During handling, edges, corners and projections on these irregularly shaped lumps break off as fines, which create problems in metallurigcal operations. For example, when coke IS used in a blast furnace, it is desirable that the bed of coke in the blast furnace be porous to permit gasses to pass upwardly through the bed of coke. Fines which break off from irregularly shaped lumps of coke tend to clog the gas passages in the bed. To prevent this problem, conventional coke was subjected to a screening operation prior to use, to remove fines (e.g., particles which would pass through a A screen).

Reactive form coke has advantages over conventional coke because reactive form coke can be made from coal not previously acceptable for making coke and because the manufacturingprocess for reactive form coke does not pollute the air as does the manufacturing process for conventional coke. Some illustrative examples of reactive form coke are described in Work et al. US. Pat. No. 3,184,293; and some illustrative examples of processes for producing reactive form coke are described in Work U.S. Pats. Nos. 3,140,241 and 3,140,242.

Reactive form coke is produced in the form of briquettes having a relatively smooth, regular shape. Because of the relatively smooth surface and regular shape of the briquettes, the breaking oif of edges, corners and projections from briquettes is minimized. However, conventionally treated briquettes of reactive form coke are relatively easily abraded during handling; and abrasion results in the removal, from the briquettes, of ultrafine particles (e.g., 5-20 microns across). These ultrafines cause a serious dusting problem during handling of the coke. The amounts of ultrafines, as a proportion of the total weight of the reactive form coke, is relatively small, substantially smaller than the amount of fines which break off on conventional coke; but the amount of ultrafines which abrade from the briquettes of reactive form coke is larger than the amount of ultrafines which break off from the irregularly shaped lumps of conventional coke.

The dusting problem, caused by the abrasion of ultrafines from the briquettes, can occur whether the briquettes are subjected to both long distance transportation and local handling, or to local handling, alone.

As a solution to the dusting problem associated with briquettes of reactive form coke, it has been suggested that the briquettes be coated, prior to handling, with a variety of films composed of alkali metal silicates, petroleum and terpene resins, petroleum and coal tar asphalts and pitches, and molasses. However, each of these film compositions has its drawbacks. For example, alkali metal silicates add ash to the reactive form coke, and this is undesirable. The resins and the pitches require the addition of surfactants to disperse them in water so as to permit application of a coating. The asphalt and molasses cause adhesion difiiculties, and extra care must be used in applying them.

It is undesirable to add water to coke, because, when the coke is added to a metallurgical processing unit, the water must be driven oif the coke before the coke can perform its function; and heat which would otherwise be useful in the metallurgical process is wasted driving off Water from the coke.

Heretofore, a conventional method of reducing dusting of carbonaceous material such as coal or conventional coke has been to apply, to the carbonaceous material, a coating of lignosulfonate (see Cole US. Pat. No. 1,924,- and Cunningham US. Pat. No. 1,988,999).

SUMMARY OF THE INVENTION A method in accordance with the present invention reduces dust during handling of briquettes of reactive form coke following processing ina coke-making unit. The method comprises removing the briquettes of reactive form coke from the coke-making unit at an elevated temperature, usually substantially above 212 F. (the boiling point of water). The hot briquettes are cooled until the individual average temperature of a briquette is less than 212 F. and above atmospheric temperature. (The individual average temperature of a briquette is the average of the temperatures along a cross section of the briquette. The core temperature of a briquette undergoing cooling is usually higher than the surface temperature, with a temperature gradient existing between the core and the surface.)

While the briquettes are undergoing cooling and are at an elevated individual average: temperature above atmospheric temperature and below 212 R, an aqueous agent is applied to the briquettes, the aqueous agent consisting essentially of at least one lignosulfonate and water. The aqueous agent, at the time of application, has a temperature substantially below the individual average temperature of the briquettes.

By applying the aqueous agent under the conditions described in the preceding paragraph, the aqueous agent is sucked into the surface-adjacent pores of a briquette, as the briquette undergoes cooling. Moreover, the briquette is at an elevated temperature which partially dries out the aqueous agent, leaving an adhesive coating of lignosulfonate behind. An adhesive coating of lignosulfonate (as distinguished from a baked, flaky coating of lignosulfonate) significantly reduces the abrasion of ultrafine particles from the briquette, thereby reducing dusting during handling.

Because the elevated briquette temperature, at which the aqueous agent is applied, is below the boiling point of water, the water in the aqueous agent is dried off rather than being rapidly boiled 01f. Rapidly boiling ofl the water would be undesirable, because it would leave essentially only the lignosulfonate on the surface of the briquettes, and the remaining lignosulfonate would be baked as the briquette continues to cool from a temperature which would rapidly boil off water. The resulting dried-out, baked coating of lignosulfonate would flake off relatively easily, and the briquette would lose it abrasionresisting coating, thus not solving the dusting problem.

In one embodiment, the step of applying aqueous agent to the briquette includes applying an aqueous agent containing an alkaline oxide (selected from the group consisting of calcium oxide and magnesium oxide) at a time no earlier than the application of the lignosulfonate. Subsequently, the alkaline oxide on the briquettes is reacted with carbon dioxide to form a carbonate in the film coating the briquettes; and such a film has improved dust-reducing properties.

Other features and advantages are inherent in the method claimed and disclosed or will become apparent from the following detailed description.

DETAILED DESCRIPTION INCLUDING PREFERRED EMBODIMENTS In a typical embodiment, reactive form coke is continuously removed from the coke-making unit, with the reactive form coke in the shape of briquettes having a relatively smooth, regular form; and the briquettes are conveyed along a predetermined path having a plurality of treating stations at spaced intervals. The temperature of the briquettes as they leave the coke-making unit is usually substantially above 212 F. (e.g., 400-600 F.).

At a first treating station, a cooling fluid is applied to cool the surface of the briquettes (e.g., by spraying). The cooling fluid may be water, steam, or an inert gas which does not react with the coke briquettes.

After application of the cooling fluid, the briquettes are permitted to cool. Usually, the surface of a given briquette has a lower temperature than the core of the briquette, with the individual average temperature of a briquette being somewhere between the core temperature and the surface temperature. The core temperature of the briquettes is permitted to drop until an individual average temperature below 212 F. is attained. This can be accomplished by moving the briquettes along the predetermined path, exposed to atmospheric temperature, with the time of movement between the cooling station and the subsequent film-applying station being sufficiently long to permit the desired drop in core temperature.

At the film-applying station, the briquettes are sprayed with, or submerged beneath, an aqueous agent consisting essentially of at least one lignosulfonate and water. If the water in the aqueous agent does not boil off upon application but begins to boil ofi thereafter, this means that the surface temperature of the briquettes was below 212 F. at the time of application but the individual average temperature was above 212 F., so that more cooling should have been permitted before application of the aqueous agent.

The aqueous agent may be a solution or dispersion of a lignosulfonate and water; Preferably, the calcium salt of lignosulfonic acid is used because calcium is a conventional additive to blast furnaces or other metallurgical processing unit in which coke is utilized. Oth'er usable lignosulfonates are the sodium, potassium and magnesium salts, for example.

Lignosulfonates are by-products in the production of paper. As such, they include other solids, principally wood sugars which comprise, for example, about of the total solids in by-product lignosulfonates. As used herein, the term lignosulfonate refers to lignosulfonate obtained as a by-product in the production of paper and usually including associated solids such as wood sugars. Following are examples of compositions (wt. percent, on a moisture-free basis) of commercial lignosulfonates usable in embodiments of the present invention.

TABLE I Example number pH, 3% solution 4.4 7.2 8. 50 3. 0-3. 5 3. 54. 0 3. 0 3.6 Total sulfur as S, pereent 5.40 5.02 5.33 5.26 5.15 5.84 5.29 Sulfate sulfur as S, percent 0.30 0.02 0.29 0.73 0. 50 0.35 0. 35 Sulfite sulfur as S, percent 0. 05 0.25 0.20 0.10 0.10 0.10 0.08 0210, percent-.. 6.34 5. 58 10.97 0.41 6. 52 5. 60 5.40 MgO, percent--. 0.37 0. 36 0.41 0.21 0.27 0.20 0.20 R203, percent- 0.07 0.07 0.07 0.09 0.09 N 820, percent 1. 71 5. 45 Trace Reducing sugars, percent--- 18. 50 19.60 3. 00 23. 20 2.0-5.0 14.2 21. 6 00113, percent- 8.20 8.40 7. 87 7.61 8. 7.74 8. 41

The proportion of lignosulfonate in the aqueous agent is in the range of about 10'50 wt. percent (preferably 3'040 wt. percent).

The lignosulfonate is applied to the briquettes in the ratio of about l060 lbs. of lignosulfonate per ton of coke, both expressed on a dry basis. Increased surface roughness and increased handling require increased lignosulfonate in the film on the briquettes, within the range specified in the preceding sentence.

The individual average temperature of the briquettes, at the time the aqueous agent is applied, is above atmospheric temperature and below 212 F., preferably in the range l00200 F.; and the temperature of the aqueous agent at the time of application is between atmospheric temperature and F., preferably at atmospheric temperature.

When the briquettes are to be used in a metallurgical process relatively immediately after the aqueous agent is applied (i.e., without any significant storage period before use), the aqueous agent is applied when the individual average temperature of the briquettes is in the range of about -200 F. Applying the aqueous agent when the briquettes are within this temperature range dries off the water, applied to the briquettes as part of the aqueous agent, before the coke is used in the metallurgical process. The drying rate is sufiiciently rapid to significantly reduce the amount of heat required to drive off water from the briquettes during the immediately-following metallurgical process. Yet, the drying rate is sufiiciently slow to avoid a baked, brittle, non-adherent film of lignosulfonate. Typically, the briquettes are used in the metallurgical process before they have cooled to atmospheric temperature.

In that embodiment of the method in which a carbonate is formed as part of the film, an additional aqueous agent, containing the alkaline oxide, is applied to the briquettes at a station downstream of the station at which the aqueous agent containing the lignosulfonate was applied; or the alkaline oxide is contained in the same aqueous agent containing the lignosulfonate. In all embodiments, the alkaline oxide is applied, in an aqueous agent, no earlier than the time at which the lignosulfonate is applied.

After application of the aqueous agent containing the alkaline oxide, the alkaline oxide is reacted with carbon dioxide to form a carbonate in the film. This can be done by placing the briquettes in a closed bin purged for up to three hours with waste combustion gases containing at least 15 vol. percent CO for example. Any other gas, containing substantially more carbon dioxide than is present in the atmosphere, may also be used.

However, if the briquettes are to be stored for a significant time before use in a metallurgical process, then the step of reacting the alkaline oxide with carbon dioxide need not be artificially induced using gases containing carbon dioxide in proportions greater than that present in the atmosphere. Instead, the carbonate will form, during the storage period, merely by the reaction of the carbon dioxide in the atmosphere with the alkaline oxide in the film.

On the other hand, if the briquettes are to be used in a metallurgical process relatively immediately after application of the dust-preventing film (i.e., without a significant storage period) then the reacting step should be performed without substantial delay after applying the calcium oxide and should be performed utilizing a gas containing substantially more carbon dioxide than that contained in the atmosphere, e.g., a gas containing at least 15 vol. percent CO For optimum results, the amount of alkaline oxide used should not exceed the weight of the lignosulfonate used. Preferably, the alkaline oxide should constitute about 60-75% of the lignosulfonate (plus associated solids) on a dry basis.

The resulting film of lignosulfonate significantly reduces the amount of ultrafines which can be abraded from the surface of the briquettes of reactive form coke, thereby significantly reducing dusting during handling. The lignosulfonates have the additional advantage of imparting very little ash to the reactive form coke, and an aqueous agent containing lignosulfonate can be sprayed with uniform distribution using a lignosulfonate concentration as high as 25%.

Briquettes of reactive form coke having a lignosulfonate film produce both less fines and less ultrafines than do briquettes of reactive form coke without the lignosulfonate film.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is: 1. A method for treating briquettes of form coke to reduce dust therefrom during handling following processing in a coke-making unit, said method comprising the steps of:

removing said briquettes from said coke-making unit at an elevated temperature substantially above 212 F.;

subjecting said briquettes to cooling until the individual average temperature of a briquette is less than 212 F. and above atmospheric temperature;

applying to said briquettes at least one aqueous agent consisting essentially of at least one lignosulfonate and water; said aqueous agent being applied while said briquettes are undergoing cooling and are at an elevated individual average temperature above atmospheric temperature and below 212 F.;

said aqueous agent, at the time of application, having a temperature substantially below the individual average temperature of said briquettes; and drying olf the water, in said aqueous agent, from said briquettes as the briquettes cool from said elevated temperature, without boiling so as to form an adherent film of lignosulfonate on said briquettes and prevent the formation of a dried-out, baked, flaky coating of lignosulfonate. 2. A method as recited in claim 1 wherein: the individual average temperature of said briquettes, a the time said aqueous agent is applied, is in the range 100200 F.;

and the temperature of said aqueous agent, at the time of application is between atmospheric temperature and 100 F.

3. A method as recited in claim 2 wherein said aqueous agent is at atmospheric temperature at the time of application.

4. A method as recited in claim 1 wherein:

said briquettes are used in a metallurgical process relatively immediately after said aqueous agent is applied,

and the individual average temperature of said briquettes, at the time said aqueous agent is applied, is in the range of about 140-200 F.

5. A method as recited in claim 4 wherein said briquettes are used in said metallurgical process before they have cooled to atmospheric temperature.

6. A method as recited in claim 1 wherein the proportion of lignosulfonate in said aqueous agent is in the range of about 10-50 wt. percent.

7. A method as recited in claim 6 wherein said proportion of lignosulfonate is in the range of about 3040 wt. percent.

8. A method as recited in claim 1 wherein said lignosulfonate is applied to said briquettes in the ratio of about 1060 lbs. of lignosulfonate per ton of coke, both expressed on a dry basis.

9. A method as recited in claim 1 wherein said step of subjecting the briquettes to cooling comprises:

apply a cooling fluid to cool the surface of said briquettes;

and then permitting the core temperature of the briquettes to drop until said individual average temperature is attained.

10. A method as recited in claim 1 wherein the step of applying aqueous agent includes applying an aqueous agent containing an alkaline oxide selected from the group consisting of CaO and MgO, at a time no earlier than the application of said lignosulfonate.

11. A method as recited in claim 10 wherein both said lignosulfonate and said alikaline oxide are included together in one aqueous agent.

12. A method as recited in claim 10 wherein said aqueous agent containing alkaline oxide is applied separately from and after application of the aqueous agent containing lignosulfonate.

13. A method as recited in claim 10 and comprising the additional step of:

reacting the alkaline oxide on said briquettes with CO to form a carbonate in said film, before using said briquettes in a metallurgical process.

14. A method as recited in claim 13, wherein:

said reacting step is performed by treating said briquettes with a gas containing substantially more CO than is contained in the atmosphere;

said reacting step is performed without substantial delay after applying said calcium oxide;

and said briquettes are used in a metallurgical process relatively immediately after said reacting step.

15. A method as recited in claim 13 wherein said gas contains at least 15 vol. percent CO References Cited UNITED STATES PATENTS 3,184,293 5/ 1965 Week et al 44-23 1,860,465 5/1932 Komarek 44-6 2,800,172 7/1957 Romer et al -42 X CARL F. DEES, Primary Examiner US. Cl. X.R. 

